1. Field of the Invention
The present invention relates to downhole oil well completion tools and more particularly to an improved carbide-coated blast tubing joint construction wherein a plurality of reduced diameter sections of the tubing afford flat surfaces that are easily gripped with wrenches, and slips easily attach to the joint and wherein the joint has a continuous carbide coating for protection in use as a blast tubing joint.
2. General Background
In the completion of an oil or gas well, a plurality of joints of tubing or pipe are connected end-to-end to form an elongated string that is placed inside a cylindrical outermost casing. Each joint of pipe typically has a pair of threaded end portions which connect the joints together. A common type of tubing includes a first internally threaded end portion and a second externally threaded end portion so that an end portion of one joint threadably attaches to an end portion of an adjacent joint by a mating of the internal and external threads. The internal threaded portion is typically referred to as the "box" end portion of the tubing or the "box" connection. The externally threaded portion of the tubing is typically referred to in the art as the "pin" end portion or the "pin" connection.
Common oil and gas well tubing sections are usually of uniform cylindrical outer configuration, being generally elongated such as, for example, twenty (20) foot, thirty (30) foot, or forty (40) foot joints, and having a relatively small diameter in comparison to the length of the joint, such as, for example three (3) inches-six (6) inches in external or overall diameter. The common commercially available joints of tubing also have a cylindrical internal bore which is uniform between the end portions of the joint, thus having a uniform cylindrical or circular cross section.
Tubing must often be used in a very hostile environment such as, for example, highly abrasive environments of well completion. In these situations, it is desirable to coat the tubing with carbide, for example, so that the tubing can better withstand the environment in which it is used. It is known in the art to coat a generally uniform cylindrical section of tubing with a carbide coating for purposes of protecting that joint of tubing in its downhole hostile environment.
After an oil or gas well is drilled, the outer cylindrical well casing is perforated using a perforating gun that is positioned at a location or elevation where the well is to be produced. The perforating gun penetrates through the casing and into the surrounding formation creating several perforations over a given vertical distance. Oil, sand, or both comes into the casing through these perforations, hits the tubing at generally right angles and can have a blasting effect such as occurs in sand blasting.
A "blast joint" of heavier dimensions was designed years ago to function in a completion situation. Whereas normal tubing is about one quarter inch (1/4) thick wall thickness, a typical prior art "blast joint" is about one-half inch (1/2) thick. The one-half inch (1/2) thickness is not always sufficient because the blast of material (including sand, oil, and formation material) coming from the perforations and hitting the tubing can still mechanically erode or cut it and wash it out.